Xu Huan, Yang Zhen, Li Hailing, Gao Zhonghong
Hubei Key Laboratory of Bioinorganic Chemistry and Materia Medica, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, 430074, People's Republic of China.
Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas, 77004, United States.
Chemistry. 2017 Dec 14;23(70):17755-17763. doi: 10.1002/chem.201703455. Epub 2017 Nov 22.
Protein tyrosine nitration is implicated in the occurrence and progression of pathological conditions involving free radical reactions. It is well recognized that hemin can catalyze protein tyrosine nitration in the presence of nitrite and hydrogen peroxide. Generally, the catalytic efficiency is positively correlated to its peroxidase activity. In this study, however, it is found that the efficiency of hemin in catalyzing protein tyrosine nitration is largely suppressed after functionalization with graphene derivatives, even though its peroxidase-like activity is more than quadrupled. Further studies show that the oxidation of tyrosine is still observed for these composites; dityrosine formation, however, is greatly inhibited. Furthermore, these composites also exhibit strong effects on the oxidation of nitrite into nitrate. Therefore, we propose a mechanism in which hemin-graphene derivatives facilitate the oxidation of tyrosine and nitrite to produce tyrosyl radicals and nitrogen dioxide radicals in the presence of hydrogen peroxide, but graphene interlayers serve as barriers that hinder radical-radical coupling reactions; consequently, protein tyrosine nitration is restrained. This property of hemin-graphene derivatives, by which they catalyze substrate oxidation but suppress radical-radical coupling reactions, shows their great potential in selective oxidation procedures for byproduct removal.
蛋白质酪氨酸硝化作用与涉及自由基反应的病理状况的发生和发展有关。众所周知，在亚硝酸盐和过氧化氢存在的情况下，血红素可以催化蛋白质酪氨酸硝化作用。一般来说，催化效率与其过氧化物酶活性呈正相关。然而，在本研究中发现，用石墨烯衍生物功能化后，血红素催化蛋白质酪氨酸硝化作用的效率在很大程度上受到抑制，尽管其类过氧化物酶活性增加了四倍多。进一步的研究表明，这些复合材料仍然可以观察到酪氨酸的氧化；然而，二酪氨酸的形成受到极大抑制。此外，这些复合材料对亚硝酸盐氧化成硝酸盐也有很强的作用。因此，我们提出了一种机制，即血红素-石墨烯衍生物在过氧化氢存在的情况下促进酪氨酸和亚硝酸盐的氧化，以产生酪氨酰自由基和二氧化氮自由基，但石墨烯夹层作为阻碍自由基-自由基偶联反应的屏障；因此，蛋白质酪氨酸硝化作用受到抑制。血红素-石墨烯衍生物的这种催化底物氧化但抑制自由基-自由基偶联反应的特性，显示了它们在选择性氧化去除副产物过程中的巨大潜力。
